This invention relates to a feedback color control system and, more particularly, to a system for controlling the simultaneous application of two dyes to a continuously formed material such as a web of paper.
Continuous process color control systems are known in the prior art. Generally, such systems use tristimulus colorimeters or similar instruments to measure the tristimulus values (red, green, and blue primary components) of the light reflected from a portion of the web or other material. Each of the red, green, and blue tristimulus signals is used to provide negative feedback individually to control an appropriate dye applicator located upstream from the measuring point. An example of such a system is shown in U.S. Pat. No. 3,389,265, issued to Schreckendgust.
Systems such as that described above are not universally applicable to any two dyes. If an attempt is made to control addition of a single dye by using a measured tristimulus variable, the variable chosen for control must be changed depending on the dye used. Direct use of the measured tristimulus variable for control of the addition of two dyes has proved impracticable.
I have provided a feedback color control system which overcomes the defects of color control systems pointed out hereinabove. My system may be used without change for one or two dye control. It can be used for any combination of two dyes regardless of color. It does not require detailed information about the optical properties of the component dyes. My system utilizes optical properties which correlate extremely well with visual color assessment.